Fluid flow meter

ABSTRACT

The fluid flow meter includes a flexible membrane formed of a flexible material and containing an apparatus for providing the membrane with resilience for undulation. The membrane is mounted in the fluid flow path such that the pair of faces simultaneously define with the housing fluid impermeable seals at least two different locations along the flow path. The membrane flexes so as to permit passage of discrete quanta of fluid, each having a known volume. The flow meter generates electrical signals corresponding to flexure of the membrane, and the electrical signals are monitored for determining a fluid flow rate.

BACKGROUND OF THE INVENTION Related Applications

This is a continuation-in-part of Ser. No. 7/212,955 filed June 29,1988.Iadd., now U.S. Pat. No. 4,920,794.Iaddend..

FIELD OF THE INVENTION

The present invention relates generally to devices for measuringvolumetric fluid flow and more specifically to a flow meter having aflexible membrane which operates to permit passage of fluid intravelling waves.

DESCRIPTION OF RELATED ART

Travelling wave fluid meters generally operate by measurement of therate of undulation of a member which vibrates or undulates as fluidflows past the member. One early form of fluid meter included anundulating metallic spring confined in a fluid flow chamber and amechanical counter for indicating the amount of fluid flowingtherethrough. A more recent type of travelling wave flow meter utilizesan undulating membrane formed of piezoelectric material which generateselectrical signals as a function of the rate of undulation.

Such flow meters are generally limited in use to measurement ofnoncompressible fluids, such as liquids. A metallic spring can offerexcessive resistance to the flow of a gas, and a light membrane subjectto turbulence at high flow rates and deformation at elevatedtemperatures can introduce errors in the signal processing necessary forflow measurement with such a device.

Hence, it has been found that for a travelling wave type of flow meter,it would be desirable for a membrane providing for the travelling wavesof fluid flow to be as light as possible while effectively blocking thefree flow of fluid past the membrane, and to have permanent undulationcharacteristics. It has been found that metal foils are subject tocorrosion, and that plastic membranes tend to acquire a permanentdeformation, especially upon exposure to high temperatures, interferingwith undulation of the membrane. It would also be desirable to provide atravelling wave membrane which would be largely unaffected by theinfluence of gravity due to positioning of the flow meter, and whichwould also have dimensional stability against twisting of the membrane,to prevent free flow past the edges of the membrane. The presentinvention fulfills these needs.

SUMMARY OF THE INVENTION

Briefly and in general terms, the invention provides for a fluid flowmeter having a flexible membrane formed of a flexible material andcontaining an apparatus providing the membrane with resilience forundulation in one axis perpendicular to the direction of flow andresisting flexing in other directions. The membrane is mounted in afluid flow path of the meter such that the faces of the membranesimultaneously define with the housing fluid impermeable seals at two ormore different locations along the flow path. The membrane is operativeto flex so as to permit passage of discrete quanta of fluid, each havinga known volume varying as a function of flow rate. Means are providedfor generating electrical signals corresponding to flexure of themembrane. Means are also provided for receiving the electrical signalsover a measured period of time, determining the rate of the electricalsignals, determining the volume of the fluid quanta based upon theelectrical signals, and thereby determining a fluid flow rat along theflow path.

According to another aspect of the invention, the apparatus forgenerating electrical signals comprises first and second piezoelectricmembers disposed, respectively, on first and second stop members onopposite sides of the membrane and in electrical communication with themonitoring apparatus and such that undulation of the membrane causes themembrane to alternatingly contact the stop members to generate anelectrical signal upon release of each quantum of fluid.

In accordance with another aspect of the invention, the monitoringapparatus includes means for identifying electrical signals generated byflexure of the membrane upon release of a single quantum of fluid, andalso preferably comprises means for alternatingly receiving theelectrical signals from the first and second piezoelectric members tofilter out signals not due to true undulation of the membrane.

These and other aspects of the invention will become apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective illustration of a quantum fluid flow meter,constructed according to an embodiment of the invention;

FIG. 2 is a sectional view of the flow meter of FIG. 1, taken along line2--2 therein;

FIG. 3 is a cross-section taken along line 3--3 in FIG. 2;

FIG. 4 is a cross-section taken along line 4--4 in FIG. 3;

FIG. 5 shows an enlarged detail of a portion of the cross-section shownin FIG. 4;

FIG. 6 shows an enlarged detail of a portion of the cross-section shownin FIG. 4, constructed according to an alternative embodiment of theinvention;

FIG. 7 is a sectional illustration of a portion of a piezoelectricmember useful in the flow meter of FIG. 1;

FIG. 8 is an enlarged cross-sectional view taken along line 8--8 in FIG.3;

FIG. 9 is a view similar to that of FIG. 8, but showing a constructionaccording to an alternative embodiment of the invention;

FIG. 10 is a view similar to that of FIG. 8, but showing a constructionaccording to a further embodiment of the invention;

FIG. 11 shows a piezoelectric member similar to that shown in FIG. 7 butwherein the ends thereof are thickened;

FIG. 12 is a cross-sectional partial view of spring mounts for guideblocks shown in FIG. 8 to 10;

FIG. 13 is an elevational view of an end portion of the piezoelectricmember shown in FIG. 3 and showing mounting details thereof;

FIG. 14 is a cutaway illustration of a portion of a side wall of thehousing of the flow meter shown in FIG. 1;

FIG. 15A, 15B and 15C show three successive stages in the transport ofdiscrete fluid quanta across the flow meter of FIG. 1;

FIG. 16 is a schematic illustration of a fluid flow meter similar tothat shown in FIG. 1, but having arched walls;

FIG. 17 is a block diagram illustration of electronic apparatusassociated with a fluid flow meter of the present invention;

FIG. 18 is a block diagram illustration showing a telemetering system,useful in conjunction with a fluid flow meter of the present invention;

FIG. 19 is a block diagram illustration showing an alternativetelemetering system, useful in conjunction with a fluid flow meter ofthe present invention;

FIG. 20 diagram illustration showing a further alternative telemeteringsystem, useful in conjunction with a fluid flow meter of the presentinvention;

FIG. 21 shows a multiplexed telemetering system, useful in conjunctionwith a fluid flow meter of the present invention;

FIG. 22 shows a partial side-section of a fluid flow meter, constructedand operative with an alternative embodiment of the invention;

FIG. 23 shows a partial side-section of a fluid flow meter, constructedand operative with a further alternative embodiment of the invention;

FIG. 24 is a top view of a piezoelectric member, constructed andoperative in accordance with an alternative embodiment of the invention;

FIG. 25 is a top view of an alternate embodiment of a flexible membrane;

FIG. 26 is a cross-sectional view of the embodiment of FIG. 25 takenalong line 26--26;

FIG. 27 is a top plan view of a further embodiment of a flexiblemembrane;

FIG. 28 is a cross-sectional view of the embodiment of FIG. 27 takenalong line 28--28;

FIG. 29 is a top plan view of a further embodiment of a flexiblemembrane;

FIG. 30 is a cross-sectional view of the embodiment of FIG. 29 takenalong line 30--30;

FIG. 31 is a top plan view of a further embodiment of a flexiblemembrane;

FIG. 32 is a cross-sectional view of a further embodiment of a flexiblemembrane;

FIG. 33 is a view similar to that of FIG. 8, but showing a constructionaccording to a further alternative embodiment of the invention;

FIG. 34 is a view similar to that of FIG. 8, but showing another furtheralternative embodiment of the invention;

FIG. 35 is a view similar to that of FIG. 3, showing a mechanism forrendering the membrane flat during periods of no-flow; and

FIG. 36 is a view similar to that of FIG. 35 showing a mechanism foradjusting the tension on the membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1, 2 and 3, a positive displacement fluid flow meter10, includes a housing 12 defining a fluid flow chamber 14 (FIG. 2)having first and second ends 16 and 20, and having respective first andsecond fluid ports 18 and 22.

Although in the shown embodiment, fluid ports 18 and 22 functionrespectively as an inlet and outlet, it will be appreciated from theensuing description that the internal arrangement of flow meter 10 issuch that fluid flow may take place in any chosen direction and with theflow meter at any preferred orientation.

According to a preferred embodiment of the invention, flow meter 10 isused for metering the flow of compressible fluids, such as gas. As,however, as the flow meter of the present invention may also be used forthe metering of noncompressible fluids such as oil or water, the flow of"fluid" is described herein throughout except where not applicable.

According to the shown embodiment, housing 12 includes a first endreceiving chamber 26 for receiving fluid flow from inlet 18 prior to thefluid passing through flow chamber 14. Chamber 26 permits any debrisand, in the case of gas flow, moisture, to be deposited therein prior toflow through flow chamber 14. There is also provided a second endchamber 27, similar to first end chamber 26, for receiving therein anydeposition of debris and moisture in a case of flow in a directionopposite to that indicated.

According to the present invention, discrete quanta of fluid, eachhaving a known volume, are permitted to pass across a membrane 35 andvolumetric flow may be determined according to the number of such quantapassing across the membrane. This is described in greater detail below.Although membrane 35 is positioned such that in a non-flow situationedges 33 thereof are very close to sidewalls 29, typically in the orderof magnitude of several scores of microns, such that leakage of anyfluid therepast is prevented, it is preferable in a flow situation, thatthe gap between the membrane edges and the sidewalls be reduced.

With reference additionally to FIGS. 4 and 5, flow chamber 14 is,therefore, provided with a pair of preferably rigid first sidewalls 30and a pair of non-rigid second sidewalls 29 fabricated of a flexibleelastomer, such as rubber. As fluid passes across membrane 35, pressureinside flow chamber 14 drops and the flexible, second sidewalls 29 tend,therefore, to move slightly inwards so as to reduce the gap betweenedges 33 of the membrane and sidewalls 29 to a fluid boundary layerthickness. Due to the high resistance to flow along the gap, leakage is,therefore, substantially prevented. The inward movement of sidewalls 29is further facilitated by spaces 31 provided adjacent to edges 33 ofmembrane 35.

Referring briefly to FIG. 6, it has been found that when secondsidewalls are not made from a flexible material, fluid leakage may besubstantially prevented by providing them with a roughened surface 32(also shown in FIG. 3).

With particular reference to FIGS. 2 and 14, sidewalls 30 are preferablycoated with a thin layer 34 of an antistatic and hydrophobic materialsuch as carbonated polyethylene. Layer 34 prevents the build-up ofstatic electricity in the flow chamber and condensation of moisture onthe sidewalls which might otherwise interfere with the flexing ofmembrane 35. As will be appreciated from the description below, theunimpeded flexing action of membrane 35 is important to maintain.According to an alternative embodiment of the invention, the sidewallsmay be made entirely from an antistatic and hydrophobic material.

With particular reference to FIG. 7, there is shown a cross-section of aportion of membrane 35. According to the shown embodiment, membrane 35is piezoelectric and comprises a thin layer 36 of piezoelectricmaterial, such as polyvinylidene fluoride and metallized surroundinglayers, referenced 38 and 42.

According to the embodiment shown in FIG. 24, membrane 35 ispiezoelectric but, as distinct from the embodiment shown in FIG. 7, thelayer 36 of piezoelectric material is overlaid, on either or both facesthereof, by discrete metallized strips 44, each having electricalconnections 45 to a pulse detector unit 66 (FIG. 17). As the membraneflexes, as shown and described below in conjunction with FIGS. 15A to15C, it is thus possible to determine the speed of wave propagationalong the flow chamber which can be used by microcontroller 70 (FIG. 17)to further "correct" the calculated volume of each quanta of fluid.

According to a preferred embodiment of the invention, membrane 35 has asubstantially vertical position within flow chamber 14. This avoidspossible unsymmetrical functioning of the membrane due to the effects ofgravity.

As shown in FIG. 2, membrane 33 is preferably longer than the length offlow chamber 14 in which it is positioned. This ensures that membrane 35takes up a wavelike position and that flat sides 42 of the membrane arein constant engagement with sidewalls 30 of the flow chamber,preferably, at at least three locations.

Referring now to FIGS. 2 and 13, it is seen that membrane 35 is,according to a preferred embodiment; secured at ends 51 thereof aboutrods 52. Each rod 52 is in turn secured to a fixed rod 54 by means of aspring 53 contained within a housing 56. This type of mounting, it willbe appreciated, permits limited longitudinal movement of the membranewithin flow chamber 14.

Referring now to FIGS. 2 and 8, rounded guide blocks 48 are provided soas to induce instability of membrane 35, it being noted that as eachquantum of fluid passes thereacross, a very rapid change of position byflexure of membrane 35 is required. Provision of the guide blocksassists in switching of the membrane from one position to another undera very low input of kinetic energy, such as occurs in gas flows. Therange of positions taken up by membrane 35 upon flexure are describedbelow in detail with reference to FIGS. 15A to 15C.

Referring briefly to FIG. 9, there is shown an alternative embodiment ofguide blocks 48 in which each of the guide blocks also has an additionallayer of rubber.

With reference to FIG. 10, there are provided fluid permeable guideextensions 60 that are attached to guide blocks 48 and constituteextensions of curved surfaces 49 thereof. Referring additionally toFIGS. 15A to 15C, it is seen that although membrane 35 generally doesnot move along the length of the flow chamber, as the discrete quanta offluid pass through the flow meter, causing the membrane to undulate,points of contact between the membrane and the flow chamber walls"travel" in the direction of fluid flow, the membrane moving by flexurefrom a first position just prior to release of a quantum of fluid, to asecond position just after release of the quantum.

Guide extensions are made, for example, from wire mesh. While notinterfering, therefore, with the fluid flow, they have configurationssimilar to the membrane in either of its two respective positions takenup just before and after release of a quantum of fluid. As the points ofcontact between the membrane and the chamber walls, which are coincidentwith the maximum points of curvature of the membrane, move along theflow chamber towards an end thereof, they leave side walls 30 and mountguide extensions 60. Extensions 60 induce a degree of instability thatcauses, under a relatively low kinetic energy input, a relatively fastchange of position of the membrane between the positions taken upthereby just before and after release of a quantum of fluid.

Although, as stated, membrane 35 generally does not move along flowchamber 14, a certain amount of relative motion does occur between themembrane and sidewalls 30 of the flow chamber. It is, therefore,important that inward-facing surfaces 37 of sidewalls 30 are verysmooth.

According to one embodiment of the invention, as stated, membrane 35 ismade from piezoelectric material. According to an alternativeembodiment, however, as shown in FIG. 10, membrane 35 is not made from apiezoelectric material but instead has mounted on it a pair ofelectrical contacts 61, each which is alternately brought, into contactwith a corresponding one of a pair of electrical contacts 63 mountedonto guide extensions 60.

It will be appreciated that as each quantum of fluid passes through flowchamber 14 and as membrane 35 switches from one position to the other,an electrical pulse is generated by contact of one of contacts 61 with acorresponding contact 63.

This embodiment has a particular advantage over a piezoelectric membraneas a discrete pulse is generated each time membrane 35 moves so as torelease a quantum of fluid. When a piezoelectric membrane is used,however, every movement thereof generates electrical signals, a changein position of the membrane being indicated simply by an increase inintensity of the signals.

According to an alternative embodiment of the invention only a singleone of each of electrical contacts 61 and 63 is provided, a single pulsethus being generated as every alternate quantum of fluid is passed. Itwill also be appreciated that contacts 61 and 63 may be incorporatedinto other embodiments of the invention, such as those illustrated inFIGS. 8 and 9. In yet a further alternative embodiment of the invention,electrical contacts 63 may be provided independently of guide blocks 48.

Referring now to FIG. 22, there is shown an alternative embodiment ofthe invention in which membrane 35 comprises a magnetic tape.Incorporated into sidewalls 30 are, preferably, a pair of magnetic heads39. As the points of contact between the membrane and sidewalls 30travel along the flow chamber, typically just as a quantum of fluid isreleased, a point of contact of membrane 35 with one of the sidewallsmoves across an adjacent head 39, thereby generating an electricalpulse.

According to the shown embodiment a signal is generated as every quantumof fluid is released while, according to an alternative embodiment, asingle magnetic head may be provided so as to indicate release ofalternate quanta of fluid.

Referring now to FIG. 23, in the shown embodiment, as with theembodiment of FIG. 22, membrane 35 comprises a magnetic tape. Accordingto the shown embodiment, however, magnetic head 39 is embedded intosecond sidewall 30 of the flow chamber, and is operative to engage aface 41 of membrane 35 as it passes in contact therewith.

According to the shown embodiment, the membrane includes a plurality ofmagnetic bands provided thereon at a known frequency, such as 5 KHz. Asface 41 passes in contact with head 39, processing apparatus 43associated therewith is operative to sense not only passage of a portionof the membrane across the head, but it is also operative to sense thefrequency at which the magnetic bands pass, and thus to determine thespeed at which the fluid is passing.

Referring to FIG. 11, membrane 35 is shown with thickened ends 46 whichmay also include additional layers 65 of piezoelectric material. Thethickened end and the additional layers of material serve to reduce thepossibility of failure of the membrane due to fatigue stresses.According to an alternative embodiment, membranse 35 may have differentcross-sectional thickness along the entire length thereof or alongselected portions thereof.

As shown in FIGS. 12 and 13, guide blocks 48 are not rigidly positionedbut are preferably secured by springs 58 to sidewalls 30 of the flowchamber.

Reference is now made to FIGS. 15A to 15C, in which there are shownsuccessive stages of fluid flow through the flow meter of the invention.Initially, a first quantum of fluid passes into the flow chamber andexerts a force on the membrane until it is forced to change position. Atthis stage, the first quantum, referenced 62a, becomes entrapped betweenthe wall of the flow chamber, the membrane and two points of contact,referenced 67, between the membrane and the flow chamber wall.

As the point of contact nearest an inlet 69 is being established, asecond quantum of fluid, referenced 62b, enters the chamber and alsoexerts a force on the membrane, travelling downstream until eventuallyit too becomes entrapped.

A third quantum of fluid, referenced 62c, enters the flow chamber andalso exerts a force on the membrane. The points of contact continue totravel downstream until the membrane moves by flexure from one positionto another, thereby releasing the first quantum of fluid and generatingan electrical pulse.

It has been found that when the membrane is in touching engagement withthe flow chamber walls at at least three locations, possible distortionof the membrane and consequent blockage of the flow chamber, such asmight otherwise result from a high rate of flow, is prevented.

Referring to FIG. 16, there is shown a flow chamber constructed inaccordance with an alternative embodiment of the invention. The flowchamber, referenced 55, comprises a pair of curved walls 64a and 64b.The curvature of chamber 55 results in instability in the positionstaken up by the membrane, which, as described above, is desirable.Although quanta of fluid flowing alongside the outer wall 64a will belarger than those flowing alongside inner wall 64b, the quantity of flowcan be determined by taking an average of the two different-sizedquanta.

Referring now to FIGS. 3 and 17, there is shown an electrical connection47 to a metallized layer of piezoelectric membrane 35 for carrying to apulse detector unit 66 (FIG. 17) electrical signals generated bymovement of the membrane. According to an embodiment of the inventionwherein membrane 35 is not piezoelectric but electrical contacts areused instead, electrical connection 47 is connected to the electricalcontacts.

When a piezoelectric membrane is used, the pulse detector unitpreferably includes signal processing electronic circuitry that isoperative to recognize a particular shape of a pulse or an electricalsignal corresponding to flexure of the membrane at the time of releaseof a quantum of fluid from outlet 22 of the fluid flow meter. It will beappreciated that it is important to be able to distinguish such pulsesfrom background signals that are constantly being generated by themembrane.

A value for the volume of each quantum of fluid is either preset orpredetermined and stored in a memory 68 of a microprocessor 70, suchthat each signal received represents the flow of a reference volume offluid through the flow meter. The microprocessor preferably also has adisplay 72 and a serial communication port 74.

According to a preferred embodiment of the invention, by using thepreset value for each quantum and according to electrical signalsreceived, the microprocessor is operative to calculate the flow rate. Byusing flow delivery data, as are typically contained in a look-up table,and by comparing the preset quantum value with a quantum value in thetable corresponding to the calculated flow rate, the microprocessor isoperative to alter the preset quantum value to a different value. Byrepeating these steps of calculating and comparing, in iterativefashion, the microprocessor is operative to reach a "true" quantum valueand, hence, a true flow value.

Also, according to a preferred embodiment of the invention, pressure andtemperature sensors, respectively referenced 108 and 110 (FIG. 17), aremounted in the flow chamber and are effective to continuously provide tothe microprocessor pressure and temperature readings. The microprocessoralso calculates any necessary adjustment of the preset value for thevolume of each quantity of fluid, according to the pressure andtemperature data received.

The pressure and temperature readings may also be used bymicrocontroller 70 to provide an alarm indication when the temperaturerises to a dangerously high level, which may indicate fire or where thepressure drops below a predetermined threshold value, which may serve asan indication of leakage in the system.

According to an alternative embodiment of the invention, multiple flowmeters may be provided to accommodate a very large fluid flow, with theflow pulse signals being directed to a central microcontroller fordetermination of the overall fluid flow rate.

Reference is now made to FIG. 18, wherein there is shown, in blockdiagram form, centralized data collection apparatus utilizing the flowmeter of the present invention. In accordance with a preferredembodiment of the invention, a dialer 78, which permits communicationbetween the flow meter and a domestic telephone line 81, is operative toautomatically dial a data center 106 and to send thereto informationpertaining to fluid flow as measured by the meter.

A timer 76 may also be provided to trigger dialer 78 at a giveninterval, such as once a month and preferably at a time when thetelephone line is unlikely to be in use. The dialer is also preferablyoperative to continue dialing from the time it is triggered by timer 76,until it manages to get through to data center 106 and pass the requiredinformation. In the event that the connection is broken while theinformation is being passed, dialer 78 is operative to redial, ifnecessary repeatedly, until the information is successfully passed.

Referring now to FIG. 19, communication between the flow meter and amini-terminal 86 may be provided by means of a firstreceiver-transmitter 82 linked to the flow meter and a secondreceiver-transmitter 84 associated with the mini-terminal. Themini-terminal may also be equipped with a memory bank 88 and a displaypanel 90. Local networks of an optically-isolated unit 92 may beprovided through a connector 94 to a mini-terminal 96, as shown in FIG.20.

Referring to FIG. 21, fluid meters 10, which, according to a preferredembodiment are gas flow meters, may be connected with a remote datacenter 106 by means of a modem 104. This permits not only regularsending of flow information from the gas meters to the data center, butit also permits data center initiated scanning of the gas meters.

As illustrated in FIGS. 25 and 26, another embodiment of the membrane isa membrane 115 formed of an upper layer 116 and a lower layer 118 bondedtogether along their lateral, longitudinal edges 120, typically eitherby heat sealing or by adhesive. Since it is desirable for the membraneto be as light as possible in order to be able to perform in anyposition with the least effect from gravity, the flexible layers ofmembrane may be typically formed to each have a thickness ofapproximately 5 microns. In this embodiment the membrane material can becomposed of a flexible plastic and may for example be formed ofpolyethylene. Other types of thermoplastic or thermosetting plastics mayalso be suitable. A wide variety of plastics have been found to behavelike a thermoplastic, deforming under high temperatures, therebyinterferring with the natural flexing undulation of the material, andeven deforming sufficiently to block fluid flow. Although metal foilsresist deformation due to exposure to high heat, such metal foils arealso subject to corrosion, and tend to crack and fail eventually. It hasbeen found that placement of strips 122 a, b, c of a flexible materialwhich retains undulation characteristics even at high temperatureswithin the envelope formed by the upper and lower layers of thetwo-layer membrane allows the membrane to retain its undulationcharacteristics even at high temperatures, to retain corrosionresistance, and allows the membrane to be formed with extremely thinlayers of flexible plastic material. The strips 122 are typically formedof glass fibers such as optical fibers, but may also be formed ofgraphite fibers, fabric fibers, or can even be formed by thin metalstrips.

Referring to FIGS. 27 and 28, another form of the flexible membraneutilizing a single layer of flexible material 125 similar to thematerial used in the double-layer membrane 115, includes multiple strips132 a, b, c, d mounted on the outer lengthwise edges of the membrane.Other strips could also be mounted at other locations lengthwise alongthe membrane, and the housing 126 is formed with corresponding innerchannels 128, inset in the housing to form guides for the undulationmotion of the strips. The strips are mounted at the edges 130 of themembrane. These strips 132 may similarly be formed of glass fibers,graphite fibers, fabric, metal strips, or the like, and are preferablybonded to the outer surface of the membrane, as by adhesive. In theembodiment on FIGS. 25 and 26, the strips 122 are preferably only bondedto the membrane at the longitudinal ends 114 a, b of the membrane. Itshould also be recognized that the strips of heat resistant flexingmaterial can be formed either in rectilinear shapes, or in curvedshapes, or can be formed to have varying thicknesses along their length,in order to modify and adapt the flexing characteristics of themembranes.

Another form of a two-layer membrane is illustrated in FIGS. 29 and 30,showing an elongated coil of heat resistant fiber material placed withina sealed envelope formed between the two layers of the membrane 115. Thecoil 134 naturally expands to be located around the inner periphery ofthe envelope, and in particular extends along the inner longitudinaledges 120 of the membrane. The elongated fiber is preferably a loosecoil within the membrane, and is typically formed of glass fibers, suchas optical fibers, although graphite and fabric fibers are alsosuitable.

In order to create a membrane having different elasticity along thelength of the membrane, the coil 134 can be tied together at regularintervals along the length of the membrane by fiber connecting ties 135.Thus, it will be appreciated that the portion of the coil 136 betweenthe longitudinally extending portion of the coil 137 at the connectingties and the longitudinally extending portion of the coil 138 at theinner periphery of the membrane envelope is more resistive tolongitudinal flexing of the membrane, which can enhance the regular,flexing, pulsing undulation characteristics of the membrane.

Still yet another form of a membrane with supporting fibers or strips toenable the membrane to retain its undulation characteristics is shown inFIG. 32. The single membrane layer 140 includes multiple inner channels142, loosely containing elongated fibers 144, similar to the fibersreferred to above. These fibers 144 are also preferably only bonded tothe longitudinal ends 114 a, b of the membrane, to allow for freeflexing of the membrane. Such a single layer membrane as is shown inFIG. 32 is typically approximately 60 microns thick.

It has also been found that flexing of the membrane in response to fluidflow through the flow meter may also produce vibration of the membranenot corresponding to individual quanta of fluid flow, making itdifficult for the signal processing circuitry to distinguish betweensignal pulses representing quanta of fluid flow and vibrations,particularly at high fluid flow rates, which can induce turbulent flowin the meter.

One embodiment of the flow meter which is particularly useful in helpingto discriminate between signal pulses representing quanta of fluid flowand vibrational pulses is illustrated in FIG. 3. Here, a double layermembrane having the upper layer 116 and the lower layer 118 with themiddle layer of flexing supporting material 122 therebetween extendsbetween guideblocks 148, having stopper members 150 mounted to andextending from the inner surfaces 151 of the upper and lowerguideblocks. The stopper members thus serve as extension guides, andalso limit the flexing motion of the, membrane, which strikes thestopper members sequentially as it flexes. The stopper members aretypically currently formed of thin leaf springs. Piezoelectric elements152 a, b are mounted at the longitudinal ends 153, and preferably on theouter surfaces of the leaf spring stopper members. Thus, the alternatingflexing of the membrane causes the membrane to strike the stoppermembers, causing the piezoelectric elements to sequentially generatesignal pulses representing the passage of a quantum of fluid flow. Thepiezoelectric elements are in electrical communication with the pulsedetector of the signal processing circuitry, as shown in FIG. 17.

In order to further discriminate the signals due to vibrations of themembrane as it strikes the stopper members, from signal pulses due topassage of quanta of fluid flow, a discriminator circuit 156 is includedin the pulse detector, to generally pass signals over a predeterminedthreshold, which passes the received signals to a flip-flop circuit 158,which operates to pass individual pulse signals in alternating sequencefrom the first and second piezoelectric elements, to the microcontroller70.

Another arrangement of a membrane between stopper members to cause apiezoelectric element to generate signal pulses principaly when themembrane strikes the stopper members is shown in FIG. 34. Here, thearrangement is similar to that shown in FIG. 33, except that thepiezoelectric element 154 is in the form of a piezoelectric film orlayer mounted to the membrane. The piezoelectric film can be mounted onone outside surface of the membrane, as is shown in FIG. 34, or can becontained loosely within the two layers of the membrane envelope, sothat as the membrane undulates from a first position striking a firststopper member to a second position striking a second stopper member,the piezoelectric element sequentially generates electrical pulsesrepresenting passage of quanta of fluid flow. Thus, in the embodimentshown in FIG. 33, the piezoelectric signals are not a measure of bendingper se of the membrane, and only represent striking of the membrane onthe stopper members, where as in FIG. 34, the main signal from thepiezoelectric material comes from the striking of the membrane againstthe stopper member, but also is generated by bending and vibration ofthe membrane. In the case in which the piezoelectric film is bonded tothe membrane, the piezoelectric element is preferably bonded with anelastic adhesive, allowing the piezoelectric material to flex with themembrane.

As mentioned previously, one of the problems associated with operationof the fluid flow meter at elevated temperatures is the creation ofpermanent curvature of the membrane. This permanent curvature of themembrane can also be caused under conditions of no flow, so that it mayalso be desirable to maintain the membrane in a fully flattenedcondition during periods of no flow or minimal flow. A minimum flowcondition in a natural gas distribution system may merely involve thequantity of flow consumed by pilot flames, for example. One embodimentof the flow meter which can cause the membrane to become flattenedduring periods of no flow to help prevent permanent deformation of themembrane is illustrated in FIG. 35. An inner antechamber 156 isprovided, which is connected to and in fluid communication with thefluid inlet port 18. The inner antechamber is defined by the antechamberhousing 157, generally comprising an angled member, directing the fluidflow toward a diaphragm 158 positioned at the outlet of the innerantechamber, and connected to the main housing wall by a relatively weakcompression spring 160. One end of a lever arm 162 is also connected tothe spring, with the lever arm pivoting about the pivot point 164mounted to the housing, and with the other end of the lever armconnected to the upstream end of the membrane spring mounting 166. Undera condition of no flow, the diaphragm is pressed against the diaphragmlimit stops 168 on the inner antechamber housing, pivoting the lever armso that the end of the membrane is pulled sufficiently taut to flattenthe membrane. The spring 160 is sufficiently weak that a minimal fluidflow through the inlet port can dislodge the diaphragm from thediaphragm limit stops, to allow the flow meter to function.

Another similar embodiment of a mechanism for maintaining the membranein a flattened condition during periods of no flow is illustrated inFIG. 36. An inner antechamber 156 is also in fluid communication withthe fluid inlet port 18, with the inner antechamber being formed by theantechamber housing 157. A diaphragm 158 is moved in the direction offluid flow when the quantity of fluid flow exceeds a minimum threshold,and the diaphragm is pressed up against the diaphragm limit stops 168 onthe antechamber housing by the tension spring 160, connected between thediaphragm and the flow meter housing. The diaphragm is also connected tothe upstream end of the membrane spring mounting. This mechanismoperates in a fashion similar to the mechanism of FIG. 35, withoutpivoting of a lever arm.

In order to adaptively change the distance between the spring mountingclamps at the ends of the membrane to compensate for the tendency ofhigher How rate to increase the degree of curvature of the membrane, amechanism similar to a mechanism for flattening the membrane at theupstream end of the membrane may also be provided at the downstream endof the membrane. In the embodiment illustrated in FIG. 36, a cupped orparabolic drogue member 170 is attached to the clamp at the downstreamend of the membrane spring mounting 172, and is further attached to thehousing of the flow meter by a tension spring 174. At increasing flowrates, the drogue member will therefore exert an increasing tension onthe membrane, to oppose the tendency of the membrane to be increasinglycurved at the higher flow rates.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been shown and describedhereinabove. The scope of the invention is, rather, limited solely bythe claims, which follow.

I claim:
 1. A fluid flow meter, comprising:a housing having a pair offluid ports and defining a fluid flow path therebetween; a flexiblemembrane extending lengthwise in the direction of fluid flow and mountedfor flexure at opposing longitudinal ends of the membrane within thehousing, said membrane having a pair of opposing faces and two oppositeside edges extending generally in the direction of fluid flow mounted inthe fluid flow path such that the side edges form seals with saidhousing, and the pair of faces simultaneously define with the housingfluid impermeable seals at least two different locations along the flowpath operative to flex so as to permit passage of discrete quanta offluid, each quantum of fluid having a known volume varying as a functionof flow rate; at least one elongated resilient member disposed withinsaid membrane forming a plurality of lines of resilience extendingbetween said longitudinal ends of said membrane in the direction of saidfluid flow path for providing the membrane with resilience forundulation of flexing; means for generating electrical signalscorresponding to flexure of said membrane; and monitoring means forreceiving the electrical signals from said means for generatingelectrical signals over a period of time determining the rate of saidelectric signals, determining the volume of said quanta based upon saidelectrical signal rate, and thereby determining a fluid flow rate alongsaid flow path.
 2. The flow meter of claim 1, wherein said flexiblemembrane is formed of at least one layer of flexible material.
 3. Theflow meter of claim 2, wherein said flexible membrane is formed of twolayers of flexible material sealingly bonded together about theirperimeters.
 4. The flow meter of claim 2, wherein said flexible membraneis formed of a tube of flexible material having two opposite endopenings sealingly bonded together.
 5. The flow meter of claim 2,wherein said flexible membrane is formed of a sheet of flexible materialhaving internal channels extending lengthwise in the direction of saidfluid flow path.
 6. The flow meter of claim 2, wherein said flexiblematerial is non-resilient.
 7. The flow meter of claim 1, wherein said atleast one elongated resilient member comprises a plurality of elongatedresilient strips are secured to at least one longitudinal end of saidmembrane extending in the direction of fluid flow.
 8. The flow meter ofclaim 7, wherein said strips are rectilinear in shape.
 9. The flow meterof claim 7, wherein said strips vary in thickness in at least onedimension.
 10. The flow meter of claim 7, wherein said flexible membraneis formed of two layers of flexible material sealingly bonded togetherabout their perimeters, and wherein said strips are enclosed betweensaid layers of flexible material.
 11. The flow meter of claim 10,wherein said strips are bonded over the length of said strips to atleast one of said layers of flexible material.
 12. The flow meter ofclaim 1, wherein said at least one resilient member comprises elongatedfiber material.
 13. The flow meter of claim 12, wherein said membrane isformed of a sheet of flexible material having at least one internalchannel extending lengthwise in said membrane, and said fiber materialis enclosed in at least one said internal channel.
 14. The flow memberof claim 1, wherein said at least one resilient member comprises a coilof an elongated fiber material enclosed between two layers of flexiblematerial, and at least a portion of said coil extends from one of saidside edges to the other of said side edges.
 15. The flow meter of claim14, wherein opposite sides of said coil are secured together at at leastone location.
 16. The flow meter of claim 1, wherein said means forgenerating electrical signals corresponding to flexure of said membraneincludes stop means adjacent to at least one of said faces.
 17. The flowmeter of claim 16, wherein said stop means comprises at least onestopper member mounted on a guide member mounted within said housingadjacent a longitudinal end of said flexible membrane.
 18. The flowmeter of claim 16, wherein said stop means comprises a pair of stoppermembers mounted within said housing adjacent said membrane faces,respectively.
 19. The flow meter of claim 18, wherein said flexiblemembrane has first and second longitudinal ends, and further includingat least one pair of guide members mounted within said housing adjacentone of said ends of said flexible membrane, and wherein said stoppermembers each comprise a leaf spring mounted to one of said guidemembers.
 20. The flow meter of claim 16, wherein said means forgenerating electrical signals further includes piezoelectric materialmounted within said housing such that undulation of said membrane causessaid membrane to strike said stop means, causing said piezoelectricmaterial to generate an electrical signal.
 21. The flow meter of claim20, wherein said stop means comprises a stopper member mounted in aguide member in said housing adjacent said membrane, and saidpiezoelectric material is mounted on at least one said stopper member.22. The flow meter of claim 20, wherein said piezoelectric material ismounted on at least one face of said flexible membrane.
 23. The flowmeter of claim 1, wherein said membrane moves by flexure from a firstposition prior to release of a quantum of fluid to a second positionafter release of the quantum of fluid, and wherein said monitoring meansincludes pulse detector means for receiving pulse signals from a firstpiezoelectric element mounted for detection of flexure of said membraneto said first position and for receiving pulse signals from a secondpiezoelectric element mounted for detection of flexure of said membraneto said second position.
 24. The flow meter of claim 23, wherein saidmonitoring means includes signal processing means, and said pulsedetector means includes flip flop means for passing individual pulsesignals in alternating sequence from said first and second piezoelectricelements to said signal processing means. .Iadd.
 25. A fluid flow meter,comprising:a housing having an inlet and an outlet fluid port defining afluid flow path therebetween; a flexible membrane mounted at first andsecond longitudinal ends within the housing, said membrane having a pairof opposite side edges extending in the direction of the fluid flow pathto form seals with the housing; resilient guide means mounted adjacentsaid first longitudinal end for facilitating change of position of themembrane; and means responsive to membrane flexure for determining afluid flow rate along said flow path. .Iaddend. .Iadd.
 26. The fluidmeter of claim 25, wherein said guide means further comprises:a guideextension adjacent said first longitudinal end. .Iaddend. .Iadd.27. Thefluid flow meter of claim 26, wherein said guide extension is permeable..Iaddend. .Iadd.28. The fluid flow meter of claim 26, wherein said guideextension further comprises: a thin leaf spring. .Iaddend. .Iadd.29. Thefluid flow meter of claim 26, wherein said guide means furthercomprises:a pair of guide members mounted within said housing adjacentsaid inlet fluid port. .Iaddend. .Iadd.30. The fluid flow meter of claim26, further comprising: second guide means mounted within said housingadjacent said second longitudinal end of said membrane. .Iaddend..Iadd.31. The fluid flow meter of claim 30, wherein said second guidemeans further comprises: permeable guide extensions. .Iaddend. .Iadd.32.The fluid flow meter of claim 31, wherein said second guide meansfurther comprise: thin leaf springs. .Iaddend.